Spectrex Quasar 900 Open-Path Gas Detection System - Manual (Page 17)

TM 888200 Rev (I), January 2014
Principle of Operation 5
2.3.3 Optical Path
The presence of hazardous airborne vapors, gases, or aerosols in a
monitored area is detected when the defined substance crosses/enters the
optical path between the radiation source unit and the detector.
Hazardous gases /vapors present in the atmosphere cause absorption of the
radiation pulse in the optical path between the radiating source and the
detector unit at some specific wavelengths. This causes a change in the
signal intensity received by the detector, which is translated into an output
related to the detector’s measuring scale.
The system analyzes the defined open path at the spectral bands specific to
the materials being monitored. The Automatic Gain Control (AGC) unit
compensates for environmental disturbances such as fog, rain, etc., through
a constant comparison with its dual spectral beam.
2.3.4 Microprocessor Based
The incoming signals are analyzed by the built in microprocessor.
A sophisticated mathematical algorithm calculates between the various
functions of the detected signal thresholds. Statistics, ratio algorithms, data
communications, diagnostics and other functions are performed.
2.3.5 Gas Sensitivity
The SafEye Quasar 900 Model uses wavelengths around 2.3µ spectral band
to measure air flammability potential between the source and detector. At
this wavelength, all hydrocarbon materials have an absorption peak. This
enables the detector to achieve both regular sensitivity of 0-5 LEL.m.
The Quasar 900 detects hydrocarbon gases including methane, ethylene,
propane, ethane, butane, and so on.
2.3.6 Gas Calibration
The Quasar 900 has three calibrations that can be changed by function
Setup:
 Gas 1 – 100% methane
 Gas 2 – 100% propane
 Gas 3 – 100% ethylene
The full scale of methane and propane is 5 LEL.m.
The full scale of ethylene is 8 LEL.m.
2.3.7 Flash Source
The Xenon Flash Source was originally introduced in the first SafEye
development and was designed to overcome false alarms, which were
experienced by early generations of the open path system. The new SafEye
Quasar 900 employs the latest generation of flash bulbs to provide even
more power and extended operation life (10 years).